How to clean a water butt

Inspired by a UK allotment guide. This walk-through draws on the video "How To Clean Water Butts" by Allotment Book, a UK gardening channel run by allotmentbook.co.uk. They cover the risks of stored water and a clear step-by-step cleaning process that is worth watching before you start.

1. Empty the butt completely before you do anything else

Use the stored water on the garden first rather than wasting it. Run it through a hose or fill watering cans, but get it all out. The cleaning process involves disinfectant, so nothing you drain afterwards is suitable for plants until the butt has been fully rinsed.

If the butt has a tap at the base, open it fully. Tip the butt slightly once the flow slows to get the last few litres out.

2. Disconnect the downpipe diverter

Most water butts connect to the downpipe via a plastic diverter that diverts rainwater into the butt when it is not full, and sends overflow back down the drain. Twist or unclip the diverter from the downpipe so rainwater bypasses the butt while you clean it.

While you have it off, rinse the diverter under a tap and check the mesh filter is not blocked with leaf debris.

3. Scoop out the loose sludge at the bottom

There will almost always be a layer of dark sediment at the base. It is harmless in small amounts, but it is what breeds the bacteria that cause problems. Scoop it out with an old trowel or a small bucket.

Do not pour sludgy water down the drain if you can help it. Spread it on the compost heap instead.

4. Scrub the inside walls and base

Fill the butt with a few inches of clean water and get a stiff long-handled brush in there. Scrub around the walls to dislodge the algae film, which typically looks greenish or dark brown and feels slimy.

Pay attention to the corners around the tap fitting and the base. Drain and repeat if the water coming out is still very murky.

5. Mix a diluted bleach solution and fill the butt

Add roughly 35ml of household bleach per 10 litres of water. That is about a capful per bucket. Fill the butt to roughly a quarter full, swirl it around, and leave it for an hour.

This kills off any lingering bacteria and algae spores. Wear rubber gloves when handling the bleach mix. The smell will be obvious but mild at this concentration.

6. Drain and rinse thoroughly

Open the tap and let the bleach solution drain away from plants and paving. Once empty, refill with plain water, swill it around, and drain again. Repeat twice, or until there is no bleach smell left.

It is important to rinse well. Trace bleach in stored water will not harm most established plants, but it is worth being thorough given that butts are often used for seedlings and sensitive plants.

7. Check the tap, lid, and overflow connection

While the butt is empty, check the tap turns freely and does not drip when closed. If it is stiff, a smear of silicone grease on the thread usually frees it up. If it leaks at the joint, the rubber washer behind the fitting may need replacing.

Check the lid fits well to keep mosquitoes out and reduce algae growth. Algae need light to grow, so a good tight lid makes the next clean much easier.

8. Reconnect the diverter and leave the butt to fill

Refit the downpipe diverter, making sure it clicks or seats properly. Leave the tap closed so the butt fills with the next rain. It might take a few days depending on the weather, though that is not exactly a surprise in England.

If you noticed the diverter was slow to flow during the last season, now is a good time to fit a wider-bore version or clean out the downpipe above it.

When to call a handyman

Call Richard if the tap is seized beyond freeing by hand, if the butt has cracked and needs replacing, or if you want a second butt plumbed in from the same downpipe. Linking two butts gives you a lot more storage for very little extra work.